Method for fabricating semiconductor structure with strengthened patterns

ABSTRACT

The disclosure provides a method for fabricating a semiconductor structure with strengthened patterns. The method includes forming a masking layer on the substrate, the masking layer including a peripheral region and an array region adjacent to the peripheral region; forming a first etched peripheral pattern in the peripheral region and a first etched array pattern in the array region, wherein the first etched peripheral pattern and the first etched array pattern have a top surface, a sidewall and a bottom surface, the sidewall connecting the top surface to the bottom surface; forming a second peripheral pattern on the first etched peripheral pattern and forming a second array pattern on the first etched array pattern; and etching the masking layer using the first etched peripheral pattern and the second peripheral pattern as an etching mask to form an etched masking layer in the peripheral region.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Non-Provisionalapplication Ser. No. 17/000,921 filed on Aug. 24, 2020, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a method for fabricating asemiconductor structure, and more particularly, to a method forfabricating a semiconductor structure with strengthened patterns.

DISCUSSION OF THE BACKGROUND

Semiconductor devices are essential for many modern applications. Withthe advancement of electronic technology, semiconductor structures arebecoming smaller in size while providing greater functionality andcomprising greater amounts of integrated circuitry (IC).

Lithography is a process that uses photoresist as a mask to createpatterned structures. Therefore, the robustness of photoresist is ofgreat importance to pattern definition. As advancing technology drivescontinuous size reduction, various technical problems arise. Forexample, some semiconductor structures cannot be successfully formedbecause of their miniaturized size, and some semiconductor structuressuffer from defects, e.g., photoresists that are difficult to remove.

Thus, there is a need to improve the semiconductor manufacturingprocess, particularly the lithography process.

This Discussion of the Background section is provided for backgroundinformation only. The statements in this Discussion of the Backgroundare not an admission that the subject matter disclosed in this sectionconstitutes prior art to the present disclosure, and no part of thisDiscussion of the Background section may be used as an admission thatany part of this application, including this Discussion of theBackground section, constitutes prior art to the present disclosure.

SUMMARY

One aspect of the present disclosure provides a method for fabricating asemiconductor structure. The method comprises providing a substrate;forming a masking layer on the substrate, the masking layer including aperipheral region and an array region adjacent to the peripheral region;forming a first etched peripheral pattern in the peripheral region and afirst etched array pattern in the array region, wherein the first etchedperipheral pattern and the first etched array pattern have a topsurface, a sidewall and a bottom surface, the sidewall connecting thetop surface to the bottom surface; forming a second peripheral patternon the first etched peripheral pattern and forming a second arraypattern on the first etched array pattern; and etching the masking layerusing the first etched peripheral pattern and the second peripheralpattern as an etching mask to form an etched masking layer in theperipheral region.

In some embodiments, the substrate comprises a metal layer.

In some embodiments, the masking layer comprises a nitride layer.

In some embodiments, the forming the first etched peripheral pattern andthe first etched array pattern includes: forming a first photoresistlayer on the masking layer; and exposing the first photoresist layer toultraviolet radiation via a first photo mask, wherein the first photomask comprises a first transparent portion and a first opaque portioncorresponding to the first etched peripheral pattern and the firstetched array pattern.

In some embodiments, after the first photoresist layer is exposed toultraviolet radiation, a developing process is performed to form a firstpattern.

In some embodiments, the first pattern comprises a first peripheralpattern in the peripheral region and a first array pattern in the arrayregion.

In some embodiments, after the developing process is performed, anetching process is performed using the first pattern as an etching maskto form the first etched peripheral pattern and the first etched arraypattern.

In some embodiments, the forming the second peripheral pattern and thesecond array pattern includes: forming a second photoresist layer on thefirst etched peripheral pattern and on the first etched array pattern;and exposing the second photoresist layer to ultraviolet radiation via asecond photo mask, wherein the second photo mask comprises a secondtransparent portion and a second opaque portion corresponding to thesecond peripheral pattern.

In some embodiments, the forming the second photoresist layer includescovering the first etched peripheral pattern and the first etched arraypattern with the second photoresist layer.

In some embodiments, after the second photoresist layer is exposed toultraviolet radiation, a developing process is performed to form thesecond peripheral pattern and the second array pattern.

In some embodiments, the second peripheral pattern is formed on thebottom surface and separated from the sidewall of the first etchedperipheral pattern in the peripheral region.

In some embodiments, the second array pattern covers the top surface andthe bottom surface of the first etched array pattern in the arrayregion.

In some embodiments, a first pitch of the first etched peripheralpattern is different from a second pitch of the first etched arraypattern.

In some embodiments, a first height of the second peripheral pattern isgreater than a second height of the first etched peripheral pattern.

Another aspect of the present disclosure provides a semiconductorstructure. The semiconductor structure comprises a substrate including aperipheral region and an array region adjacent to the peripheral region.A first etched pattern is on the substrate, wherein the first etchedpattern includes a first etched peripheral pattern and a first etchedarray pattern, the first etched peripheral pattern and the first etchedarray pattern having a top surface, a sidewall and a bottom surface, thesidewall connecting the top surface to the bottom surface. A secondperipheral pattern is formed in the peripheral region. A second arraypattern is formed in the array region.

In some embodiments, the second peripheral pattern is formed on thebottom surface and separated from the sidewall of the first etchedperipheral pattern.

In some embodiments, the second array pattern covers the top surface andthe bottom surface of the first etched array pattern.

In some embodiments, the substrate comprises a metal layer.

In some embodiments, a first pitch of the first etched peripheralpattern is different from a second pitch of the first etched arraypattern.

In some embodiments, a first height of the second peripheral pattern isgreater than a second height of the first etched peripheral pattern.

With the above-mentioned method for fabricating a semiconductorstructure and the configuration of the semiconductor, array patterns areformed during fabrication of peripheral patterns on the metal zero (M0)layer. The fabrication of an M0 layer includes two separate processes, aperipheral region process and an array region process. The arraypatterns formed in the peripheral region process are not intended todefine profiles in the layers thereunder; instead, the array patternsserve to reduce the flow rate of developing agents. As a result, theperipheral patterns are more durable and are able to resist removal bydeveloping agents. Accordingly, during the peripheral region process,peripheral patterns do not collapse after being exposed to developingagents. Moreover, the photoresist coverage of patterns in the arrayregion is not excessive, so there is less loading effect during the etchprocesses and no hard mask remains after the hard mask strip process. Inconclusion, the formation of the array patterns contributes to formationof robust peripheral patterns.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription of the disclosure that follows may be better understood.Additional features and technical advantages of the disclosure aredescribed hereinafter, and form the subject of the claims of thedisclosure. It should be appreciated by those skilled in the art thatthe concepts and specific embodiments disclosed may be utilized as abasis for modifying or designing other structures, or processes, forcarrying out the purposes of the present disclosure. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit or scope of the disclosure as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a representative flow diagram illustrating a peripheral regionprocess for fabricating a semiconductor structure according to a firstcomparative embodiment of the present disclosure.

FIG. 2 is a schematic cross-sectional view showing the semiconductorstructure after the performing of step 101 in FIG. 1 .

FIG. 3 is an illustrative top view showing the semiconductor structureduring an intermediate stage in the fabrication of peripheral patternsaccording to a first comparative embodiment.

FIG. 4 is a schematic cross-sectional view of the semiconductorstructure of FIG. 3 according to the first comparative embodiment.

FIG. 5 is an optical microscope (OM) image of DRAM cells near a scribeline, according to an embodiment.

FIG. 6 is a picture showing a wafer after a hard mask lift-off process,according to an embodiment.

FIG. 7 is a schematic cross-sectional view showing a semiconductorstructure during an intermediate stage of the fabrication of peripheralpatterns according to a second comparative embodiment.

FIG. 8 is an SEM image showing the peripheral patterns of FIG. 7 .

FIG. 9 is an illustrative top view showing a semiconductor structureduring a developing process in an intermediate stage of the fabricationof peripheral patterns according to an embodiment of the presentdisclosure.

FIG. 10 is an illustrative diagram showing how flow of a developingagent impacts peripheral patterns.

FIG. 11 is flow diagram illustrating a peripheral region process forfabricating a semiconductor structure according to an embodiment of thepresent disclosure.

FIG. 12 is a schematic cross-sectional view showing a semiconductorstructure during a first exposure step in the peripheral region processaccording to an embodiment of the present disclosure.

FIG. 13 is an illustrative top view showing a semiconductor structureduring a first developing step in the peripheral region processaccording to an embodiment of the present disclosure.

FIG. 14 is a schematic cross-sectional view of the semiconductorstructure of FIG. 13 according to a first comparative embodiment.

FIG. 15 is an illustrative perspective view of a semiconductor structureafter the first lithography stage is completed according to anembodiment of the present disclosure.

FIG. 16 is an SEM image showing robustly-formed first peripheralpatterns according to an embodiment of the present disclosure.

FIG. 17 is a schematic cross-sectional view of the semiconductorstructure showing a first etching process during the peripheral regionprocess according to an embodiment of the present disclosure.

FIG. 18 is an enlarged view of the semiconductor structure including thefirst etched pattern of FIG. 17 according to an embodiment of thepresent disclosure.

FIG. 19 is an illustrative perspective view diagram of the semiconductorstructure after completion of the first etch stage according to anembodiment of the present disclosure.

FIG. 20 is a schematic cross-sectional view of the semiconductorstructure showing a coating step in the peripheral region processaccording to an embodiment of the present disclosure.

FIG. 21 is a schematic cross-sectional view of the semiconductorstructure showing a second exposure step in the peripheral regionprocess according to an embodiment of the present disclosure.

FIG. 22 is a schematic cross-sectional view of the semiconductorstructure showing a second developing step in the peripheral regionprocess according to an embodiment of the present disclosure.

FIG. 23 is an illustrative perspective view diagram showing thesemiconductor structure after a second lithography stage is completedaccording to an embodiment of the present disclosure.

FIG. 24 is a schematic cross-sectional view of the semiconductorstructure showing a second etching process in the peripheral regionprocess according to an embodiment of the present disclosure.

FIG. 25 is an illustrative perspective view diagram of the semiconductorstructure after the second etch stage is completed according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments, or examples, of the disclosure illustrated in the drawingsare now described using specific language. It shall be understood thatno limitation of the scope of the disclosure is hereby intended. Anyalteration or modification of the described embodiments, and any furtherapplications of principles described in this document, are to beconsidered as normally occurring to one of ordinary skill in the art towhich the disclosure relates. Reference numerals may be repeatedthroughout the embodiments, but this does not necessarily mean thatfeature(s) of one embodiment apply to another embodiment, even if theyshare the same reference numeral.

It shall be understood that, although the terms first, second, third,etc. may be used herein to describe various elements, components,regions, layers or sections, these elements, components, regions, layersor sections are not limited by these terms. Rather, these terms aremerely used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present inventive concept.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limited to thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It shall be further understood thatthe terms “comprises” and “comprising,” when used in this specification,point out the presence of stated features, integers, steps, operations,elements, or components, but do not preclude the presence or addition ofone or more other features, integers, steps, operations, elements,components, or groups thereof.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the terms “patterning” and “patterned” are used in thepresent disclosure to describe an operation of forming a predeterminedpattern on a surface. The patterning operation includes various stepsand processes and varies in accordance with different embodiments. Insome embodiments, a patterning process is adopted to pattern an existingfilm or layer. The patterning process includes forming a mask on theexisting film or layer and removing the unmasked film or layer with anetching or other removal process. The mask can be a photoresist or ahard mask. In some embodiments, a patterning process is adopted to forma patterned layer directly on a surface. The patterning process includesforming a photosensitive film on the surface, conducting a lithographyprocess, and performing a developing process. The remainingphotosensitive film is retained and integrated into the semiconductordevice.

In an advanced technology, process windows require more concerns. Thearray region and the peripheral region in a DRAM cell have differentpattern densities and serve different functions after the DRAM cellfinishes its production process. Therefore, the process windows betweenthe array region and the peripheral region vary significantly. Normally,their respective circuit patterns may not be formed at the same time.

The metal zero (M0) layer is a critical layer because it is connected tomultiple subsequent interconnect structures. In some embodiments, thefabrication of an M0 layer includes two separate processes, a peripheralregion process and an array region process. The peripheral regionprocess is used to form patterns in the peripheral region of a DRAMcell. The array region process is used to form patterns in the arrayregion of a DRAM cell. In some embodiments, the peripheral regionprocess is executed before the array region process. The peripheralregion process includes four stages: a first lithography stage (PH1), afirst etch stage (ET1), a second lithography stage (PH2) and a secondetch stage (ET2). Accordingly, the foregoing peripheral region processuses a double patterning technology (DPT) or a Litho-Etch-Litho-Etch(LELE) technique, which requires the use of two photo masks in a singlelayer. In some other embodiments, the array region process can also beperformed using an LELE technique.

FIG. 1 is a representative flow diagram illustrating a peripheral regionprocess 10 for fabricating a semiconductor structure according to afirst comparative embodiment of the present disclosure. FIG. 2 is aschematic cross-sectional view showing the semiconductor structure ofFIG. 1 , after step S101 is performed. As shown in FIG. 2 , a substrate100 is provided. In some embodiments, the substrate 100 includes a metallayer. A masking layer 102 is then deposited on the substrate 100. Insome embodiments, the masking layer 102 includes a nitride layer.Subsequently, a multilayer resist (MLR) layer 104 is deposited on themasking layer 102. The MLR layer 104 is a combination of various filmsand is used to define patterns on the substrate 100. Subsequently, ahard mask layer 106 is formed on the MLR layer 104. Finally, a firstphotoresist layer 108 is coated on the hard mask layer 106. The maskinglayer 102, the MLR layer 104, the hard mask layer 106 and the firstphotoresist layer 108 together form a multilayer film on the substrate100. The vertical dashed line in FIG. 2 indicates a boundary between aperipheral region R1 and an array region R2 in a DRAM cell. In someembodiments, the peripheral region R1 and the array region R2 includethe same multilayer film combination.

In step S103, the first photoresist layer 108 is exposed to deepultraviolet (DUV) light using a first photo mask. Because the peripheralregion process 10 is used to form patterns in the peripheral region R1,the layout in the first photo mask only corresponds to the peripheralregion R1. In fact, in the first comparative embodiment, the arrayregion R2 is not exposed to DUV light at all. Therefore, after a firstdevelopment is performed in step S105, the array region R2 is occupiedby a photoresist bulk, whereas a plurality of first photoresist patternsare formed in the peripheral region R1.

FIG. 3 is an illustrative top view depicting the semiconductor structureafter step S105 is performed. As indicated by the square dashed line,the area enclosed in the array region R2 includes a photoresist bulkPP2. The horizontal and vertical lines in the peripheral region R1indicate first photoresist patterns PP1.

FIG. 4 is a schematic cross-sectional view taken along the dashed lineA-A′ in FIG. 3 . The photoresist bulk PP2 and the first photoresistpatterns PP1 are formed and respectively located in different regions.In steps S107 to S115, the first photoresist patterns PP1 undergosubsequent processing to transfer their profiles to the layers below,while the photoresist bulk PP2 is not used for any pattern definition inthe peripheral region process 10.

Referring back to FIG. 1 , in step S109, the array region R2 is againcoated with photoresist. In steps S111 and 113, the photoresistaccumulated in the array region R2 is neither exposed nor developed. Asa result, an accumulation of photoresist in the array region R2 causes aheavy load in a photoresist strip process performed after step S115. Theheavy photoresist in the array region R2 prevents a complete photoresistlift-off, resulting in difficulty of hard mask strip. A frequent problemis that after the peripheral region process 10 is finished, the hardmask layer 106 in the array region R2 cannot be completely removed dueto photoresist remaining on the top of the hard mask layer 106.

FIG. 5 is an optical microscope (OM) image. The cross-shaped regionindicates scribe lines on the wafer. The multiple rectangular blocks areDRAM cells. Each cell has an array region R2 in the center and aperipheral region R1 surrounding the array region R2. As can be seen inthe center of multiple cells, a stain ST remains in the array region R2.Cells near the scribe line have more stains, which means a more serioushard mask remains on the cells.

FIG. 6 is a photograph showing the wafer after the hard mask stripprocess. The stain in the center of the wafer occurs due to the hardmask remaining on multiple cells.

In a second comparative embodiment of the present disclosure, theperipheral region process is similar to that of the first comparativeembodiment. As with the first comparative embodiment, the secondcomparative embodiment is also illustrated in the flow diagram in FIG. 1, with the only difference being a different layout of the first photomask formed in step S103. All the other steps are identical to those inthe first comparative embodiment. In the second comparative embodiment,the array region R2 is completely exposed to DUV light. Therefore, afterstep S105, the array region R2 is not covered by any photoresist.

FIG. 7 is a schematic cross-sectional view showing an intermediate stagein the fabrication of a semiconductor structure according to the secondcomparative embodiment. The array region R2 is free of any photoresist,whereas the peripheral region R1 has a plurality of first photoresistpatterns PP1 located on the hard mask layer 106. In the secondcomparative embodiment, the photoresist does not accumulate in the arrayregion R2. Therefore, the etch load of the array region R2 is not asheavy as that in the first comparative embodiment, thereby improving thehard mask remaining problem described in reference to the firstcomparative embodiment.

However, the process in the second comparative embodiment may not worksuccessfully, especially with a shrinking technology node. As the linewidth becomes narrower, photoresist lines become more fragile.Specifically, in the first lithography stage (PH1), first photoresistpatterns PP1 collapse after the first development process is performed(step S105).

FIG. 8 is an SEM image showing a collapse of first photoresist patternsPP1. As can be seen in the image, a portion of the vertical photoresistlines has collapsed. A suspected mechanism for the phenomenon is that,during rinsing, the developing agent may exert an unbalanced force onthe first photoresist patterns PP1. FIG. 9 is an illustrative top viewshowing a developing process in an intermediate stage of thesemiconductor structure. The curved arrows represent a flow DF of thedeveloping agent. After the developing agent is deposited onto thewafer, the subsequent rotation drives the developing agent to moveacross the wafer surface. Normally, the developing agent graduallyspreads from the wafer center to the wafer edge during the rotation.Microscopic observation of the region undergoing a developing processreveals that the developing agent flows faster in an open area.Comparing the peripheral region R1 and the array region R2, the latteris free of any impediment because no pattern is formed before or afterthe developing process. Therefore, when a developing agent with a fasterflow DF moves from the array region R2 to the peripheral region R1, astrong unbalanced force is generated. The unbalanced force arises from adeveloping agent passing from an open region (the array region R2) to acrowded region (the peripheral region R1).

FIG. 10 is an illustrative diagram showing how a developing agent flowimpacts first photoresist patterns PP1. When a developing agent DF1passes through a central channel between two neighboring firstphotoresist patterns PP1, the interior sidewalls of the firstphotoresist patterns PP1 are subjected to a capillary force F1. Thefirst photoresist patterns PP1 are pushed outward by the capillary forceF1. Similarly, when the developing agent DF2 collides with an exteriorsidewall of the first photoresist patterns PP1, the first photoresistpatterns PP1 are subjected to a striking force F2. The first photoresistpatterns PP1 are pushed inward by the striking force F2. When thestrengths of the capillary force F1 and the striking force F2 are notequivalent, the first photoresist patterns PP1 will collapse either inan outward or an inward direction.

In summary, during development, the developing agent moves back andforth between the peripheral region R1 and the array region R2. Thedeveloping agent exerts an unbalanced force on the photoresist lineswhen the wafer undergoes rotation. When the array region R2 in a cell isfree of any impediment, the unbalanced force is increased, and thereforecauses the instability of the first photoresist patterns PP1, leading totheir collapse.

The above first and second comparative embodiments suffer from differentproblems and cannot be used to fabricate robust patterns. Therefore, atrade-off solution comes from the two comparative embodiments and caneffectively solve the technical problem. According to various designs ofphoto mask layout and their corresponding experiments, a suitablepattern in the array region R2 in the first lithography stage (PH1)formed during the peripheral region process is disclosed.

FIG. 11 is a flow diagram illustrating a peripheral region process 20for fabricating a semiconductor structure according to one embodiment ofthe present disclosure. In step S200, multiple layers are formed on asubstrate 100. In some embodiments, the substrate 100 includes a metallayer. A masking layer 102 is then deposited on the substrate 100. Insome embodiments, the masking layer 102 includes a nitride layer. A MLRlayer 104 is then deposited on the masking layer 102. Subsequently, ahard mask layer 106 is formed on the MLR layer 104. With reference tostep S201 of the peripheral region process 20 in FIG. 11 , a firstphotoresist layer 108 is deposited on the hard mask layer 106.

FIG. 12 illustrates a schematic cross-sectional view of a first exposurestep in the peripheral region process 20. With reference to FIG. 12 andstep S202 of the method 20 in FIG. 11 , a first photo mask MA with afirst transparent portion 112 and a first opaque portion 114 is used.The first photoresist layer 108 is exposed to a deep ultraviolet (DUV)light 120. In some embodiments, the first photo mask MA is used to makespecific photoresist patterns in the array region R2 while theperipheral region process 20 is being performed. In some embodiments,the photo mask MA is only applied in the first lithography stage (PH1).

With reference to FIG. 13 and FIG. 14 , FIG. 14 is a schematiccross-sectional view showing a first developing step in the peripheralregion process 20 along a horizontal dashed line B-B′ in FIG. 13 . Therectangular dashed line in FIG. 13 is equivalent to the vertical dashedline in FIG. 14 , and separates the peripheral region R1 from the arrayregion R2. With reference to FIG. 13 , after step S203 of the process 20in FIG. 11 is performed, a first pattern PA is formed. The first patternPA includes first peripheral patterns PA1 and first array patterns PA2,which are separately located in the peripheral region R1 and the arrayregion R2, respectively. According to an embodiment, the first arraypatterns PA2 are formed in a grid-shaped structure, but are not limitedthereto.

In some embodiments, according to the design of the photo mask layout,the first array patterns PA2 can have different pattern densities. Thevaried photoresist pattern densities in the array region R2 have theadvantage of reducing the amount of photoresist remaining in the arrayregion R2 before the subsequent etch process is performed. The purposeof decreasing the usage of photoresist is to avoid photoresist remainingafter the completion of the double patterning of the peripheral regionR1. In addition, the first array patterns PA2 serve as an impediment,which provides a rough surface in the array region R2. When thedeveloping agent encounters a rough surface in the array region R2, themechanism for developing agents impacting on the photoresist lines ischanged. The rough surface can reduce the flow rate of developing agentswhen the wafer is rotated during the development. When the flow rate ofdeveloping agents is decreased, the capillary force received by firstperipheral patterns PA1 is also decreased. Therefore, the firstperipheral patterns PA1 can be robustly formed in the peripheral regionR1. The arrangement of the first array patterns PA2 represents acompromise between no coverage and full coverage of photoresist in thearray region R2. Such technical feature can solve both thephotoresist-remaining problem and the pattern-collapsing problem.

In some embodiments, the first peripheral patterns PA1 and the firstarray patterns PA2 serve different functions in the first lithographystage (PH1) which includes the steps S201 to S203. The first peripheralpatterns PA1 are used to define circuit patterns that are to betransferred during the final stage of the peripheral region process 20.However, the first array patterns PA2 are not intended to defineprofiles into the layers below. In some embodiments, the first arraypatterns PA2 are used to reduce the flow rate of developing agents. Thefirst array patterns PA2 assist in the formation of robust firstperipheral patterns PA1, and are not intended for pattern definition.

FIG. 15 is an illustrative perspective view diagram of the semiconductorstructure after the first lithography stage (PH1), including the stepsS201 to S203 shown in FIG. 11 , is completed. One quarter of thesemiconductor structure is the array region R2 and the other threequarters belong to the peripheral region R1. Referring to FIGS. 14 and15 , the first peripheral patterns PA1 and first array patterns PA2 arelocated in the peripheral region R1 and the array region R2,respectively, on the same hard mask layer 106. However, the two kinds ofpatterns serve different functions in the first lithography stage (PH1).First peripheral patterns PA1 are used to define circuit patterns thatare to be transferred during the final stage of the peripheral regionprocess 20. In contrast, first array patterns PA2 are not intended todefine profiles into the layers below. In some embodiments, the firstarray patterns PA2 are used to reduce the flow rate of developingagents. The first array patterns PA2 assist in the formation of robustfirst peripheral patterns PA1, and are not intended for patterndefinition.

FIG. 16 is an SEM image showing robustly-formed first peripheralpatterns PAL The photoresist patterns in the peripheral region R1 do notcollapse after the wafer undergoes development.

FIG. 17 is a schematic cross-sectional view showing a first etchingprocess in the peripheral region process 20. In step S204 of the method20 in FIG. 11 , the first etch process consumes portions of the hardmask layer 106 and portions of the MLR layer 104, which are notprotected by the first pattern PA. In some embodiments, portions of theMLR layer 104 are etched to a predetermined depth, which producesmultiple recesses in the MLR layer 104. As a result, a remaining etchedhard mask layer 106-2 and a remaining etched MLR layer 104-2 are left.

Still referring to FIG. 17 , after the first pattern PA is removed, afirst etched pattern E1, which includes the etched hard mask layer 106-2and the etched MLR layer 104-2, is formed. In addition, the first etchedpattern E1 includes a first etched peripheral pattern EA1 and a firstetched array pattern EA2, which are located respectively in theperipheral region R1 and the array region R2. In some embodiments, afirst pitch p1 of the first etched peripheral pattern EA1 is differentfrom a second pitch p2 of the first etched array pattern EA2. In someembodiments, the first etched pattern E1 has a top surface S1, asidewall S2 and a bottom surface S3, wherein the sidewall S2 connectsthe top surface S1 to the bottom surface S3. The top surface S1 is aportion of the etched hard mask layer 106-2. The sidewall S2 includes aportion of the etched hard mask layer 106-2 and a portion of the etchedMLR layer 104-2. The bottom surface S3 is a portion of the etched MLRlayer 104-2.

FIG. 18 is an enlarged view of the first etched peripheral pattern EA1in FIG. 17 . As can be seen, the etched MLR layer 104-2 includes ahorizontal MLR portion 104-2 a and a vertical MLR portion 104-2 b. Thehorizontal MLR portion 104-2 a is located on the masking layer 102, asshown in FIG. 17 . The vertical MLR portion 104-2 b is interposedbetween the horizontal MLR portion 104-2 a and the etched hard masklayer 106-2, as shown in FIG. 18 .

FIG. 19 is an illustrative perspective view diagram after the first etchstage (ET1) is completed. FIG. 19 shows the first litho-etch stage (PH1and ET1) in the patterning of the peripheral region R1 as completed. Theexposed top surface in the diagram is the top surface of the etched hardmask layer 106-2.

FIG. 20 is a schematic cross-sectional view showing a second coatingstep in the peripheral region process 20. In step S205 of the method 20in FIG. 11 , a second photoresist layer 110 is deposited on the etchedMLR layer 104-2 and etched hard mask layer 106-2. In some embodiments,the first peripheral patterns PA1, shown in FIG. 14 , are strippedbefore the deposition of the second photoresist layer 110. Inalternative embodiments, the first peripheral patterns PA1 may beremained before the deposition of the second photoresist layer 110.

Please refer to step S206 in FIG. 11 and FIG. 21 . FIG. 21 is aschematic cross-sectional view showing a second exposure step in theperipheral region process 20. The second photoresist layer 110 issubjected to a second exposure of DUV light 120 using a second photomask MB. The second photo mask MB includes a second transparent portion116 and a second opaque portion 118. It should be noted that the secondphoto mask MB serves to define patterns of peripheral circuits.Therefore, in some embodiments, the arrangement of the secondtransparent portion 116 and the second opaque portion 118 correspondsonly to the peripheral region R1.

FIG. 22 is a schematic cross-sectional view showing a second developingstep in the peripheral region process 20. In step S207 in FIG. 11 , theexposed second photoresist layer 110 is developed, and then a secondpattern PB is formed. The second pattern PB includes second peripheralpatterns PB1 and second array patterns PB2, which are separately locatedin the peripheral region R1 and the array region R2, respectively. Atthis stage, the first etched peripheral pattern EA1 originally coveredby the second photoresist layer 110 is partially exposed. In someembodiments, a first height h1 of the second peripheral pattern PB1 isgreater than a second height h2 of the first etched peripheral patternEA1. More specifically, in the peripheral region R1, the secondperipheral pattern PB1 is formed on the bottom surface S3 and separatedfrom the sidewall S2 of the first etched peripheral pattern EA1. In thearray region R2, the second array pattern PB2 completely covers the topsurface S1 and the bottom surface S3 of the first etched array patternEA2.

FIG. 23 is an illustrative perspective view diagram of the semiconductorstructure after the second lithography stage (PH2), including the stepsS205 to S207 shown in FIG. 11 , is completed. It should be noted thatthe second peripheral patterns PB1 have spaced photoresist lines, whilethe second array pattern PB2 is a full coverage of photoresist on thefirst etched pattern E1.

FIG. 24 is a schematic cross-sectional view showing a second etchingprocess in the peripheral region process 20. Please refer to step S208in FIG. 11 and FIGS. 22 and 24 . In the second etching process, themasking layer 102 is etched using the first etched pattern E1 and thesecond pattern PB, shown in FIG. 21 , as an etching mask. After theremaining photoresist is stripped, a second etched pattern E2 is formed.The second etched pattern E2 includes a second etched peripheral patternEB1 and a second etched array pattern EB2. The second etched peripheralpattern EB1 and the second etched array pattern EB2 are located in theperipheral region R1 and the array region R2, respectively. The secondetched peripheral pattern EB1 includes an etched MLR layer 104-3 and anetched masking layer 102-2. Specifically, the formation of the etchedmasking layer 102-2 is performed using the first etched peripheralpattern EA1 and the second peripheral pattern PB1, shown in FIG. 22 , asan etching mask. However, the second etched array pattern EB2 does notcontain any patterned masking layer 102 because the array region wascompletely covered by photoresist, that is, the second array pattern PB2in the second etching process. Therefore, the second litho-etch stage(PH2 and ET2) in the patterning of the peripheral region is completed.It should be noted that in the peripheral region R1, the second etchedpattern E2 has the etched masking layer 102-2, that is, the maskinglayer 102 in the peripheral region R1 is patterned. However, in thearray region R2, the masking layer 102 is not patterned at all.

FIG. 25 is an illustrative perspective view diagram of the semiconductorstructure after the second etch stage (ET2) is completed. The peripheralregion R1 has been formed by a series of patterning processes, whereasthe pattern initially defined in the first lithography stage (PH1) inthe array region R2 is not transferred to the masking layer 102.Therefore, in the array region R2, the MLR layer 104 and the maskinglayer 102 have no photoresist patterns. On the metal zero layer, thearray region process begins after the peripheral region process 20 isfinished.

In some embodiments, the peripheral region R1 has been formed by aseries of patterning processes, whereas the pattern initially defined inthe first lithography stage (PH1) in the array region R2 is nottransferred to the masking layer 102. Therefore, in the array region R2,the MLR layer 104 and the masking layer 102 have no photoresistpatterns. On the metal zero layer, the array region process begins afterthe peripheral region process 20 is finished.

The embodiments according to the invention disclose a double patterningtechnology to define peripheral patterns in a DRAM cell. Due to theconsideration of line width, the peripheral pattern lines need toundergo two lithographic processes and two etch processes. The adding ofphotoresist patterns in the array region R2 while fabricating peripheralpatterns on the M0 layer can increase the stability of peripheralpattern lines. Therefore, peripheral patterns are strengthened and areable to resist the rinse of developing agents. Peripheral pattern lineswill not collapse after being subjected to the rinse of the developingagent. Moreover, the photoresist coverage of patterns in the arrayregion is not excessive, so the loading effect is reduced during etchprocesses and, at the same time, the occurrence of photoresist residuesis avoided.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. For example,many of the processes discussed above can be implemented in differentmethodologies and replaced by other processes, or a combination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein, may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or step.

What is claimed is:
 1. A method for fabricating a semiconductorstructure, comprising: providing a substrate; forming a masking layer onthe substrate, the masking layer including a peripheral region and anarray region adjacent to the peripheral region; forming a first etchedperipheral pattern in the peripheral region and a first etched arraypattern in the array region, wherein the first etched peripheral patternand the first etched array pattern have a top surface, a sidewall and abottom surface, the sidewall connecting the top surface to the bottomsurface, wherein the first etched peripheral pattern is configured bythe steps of: configuring the top surface of the first etched peripheralpattern to have a portion of an etched hard mask layer; configuring thesidewall of the first etched peripheral pattern to have a portion of theetched hard mask layer and a portion of an etched multilayer resist(MLR) layer; and configuring the bottom surface of the first etchedperipheral pattern to have a portion of the etched MLR layer; forming asecond peripheral pattern in the peripheral region by the steps of:depositing the second peripheral pattern on the etched MLR layer at thebottom surface of the first etched peripheral pattern; in the peripheralregion, separating the second peripheral pattern from the sidewall ofthe first etched peripheral pattern, such that the second peripheralpattern is with no contact with the sidewall of the first etchedperipheral pattern; and forming a second array pattern in the arrayregion by the steps of: directly depositing the second array pattern onthe bottom surface of the first etched array pattern; and in the arrayregion, completely covering the top surface and the bottom surface ofthe first etched array pattern by the second array pattern; and etchingthe masking layer using the first etched peripheral pattern and thesecond peripheral pattern as an etching mask to form an etched maskinglayer in the peripheral region.
 2. The method according to claim 1,wherein the substrate comprises a metal layer.
 3. The method accordingto claim 1, wherein the masking layer comprises a nitride layer.
 4. Themethod according to claim 1, wherein a first pitch of the first etchedperipheral pattern is different from a second pitch of the first etchedarray pattern.
 5. The method according to claim 1, wherein a firstheight of the second peripheral pattern is greater than a second heightof the first etched peripheral pattern.
 6. The method according to claim1, wherein the forming the first etched peripheral pattern and the firstetched array pattern includes: forming a first photoresist layer on themasking layer; and exposing the first photoresist layer to ultravioletradiation via a first photo mask, wherein the first photo mask comprisesa first transparent portion and a first opaque portion corresponding tothe first etched peripheral pattern and the first etched array pattern.7. The method according to claim 6, wherein after the first photoresistlayer is exposed to ultraviolet radiation, a developing process isperformed to form a first pattern.
 8. The method according to claim 7,wherein the first pattern comprises a first peripheral pattern in theperipheral region and a first array pattern in the array region.
 9. Themethod according to claim 7, wherein after the developing process isperformed, an etching process is performed using the first pattern as anetching mask to form the first etched peripheral pattern and the firstetched array pattern.
 10. The method according to claim 1, wherein theforming the second peripheral pattern and the second array patternincludes: forming a second photoresist layer on the first etchedperipheral pattern and on the first etched array pattern; and exposingthe second photoresist layer to ultraviolet radiation via a second photomask, wherein the second photo mask comprises a second transparentportion and a second opaque portion corresponding to the secondperipheral pattern.
 11. The method according to claim 10, wherein afterthe second photoresist layer is exposed to ultraviolet radiation, adeveloping process is performed to form the second peripheral patternand the second array pattern.
 12. The method according to claim 10,wherein the forming the second photoresist layer includes covering thefirst etched peripheral pattern and the first etched array pattern withthe second photoresist layer.
 13. The method according to claim 12,wherein the second peripheral pattern is formed on the bottom surfaceand separated from the sidewall of the first etched peripheral patternin the peripheral region.
 14. The method according to claim 12, whereinthe second array pattern covers the top surface and the bottom surfaceof the first etched array pattern in the array region.